Mucin1 N-domain variant contributes to dry eye syndrome in diabetes by increasing immature mucus secretory granules.

BACKGROUND

Diabetes-associated dry eye syndrome (DMDES) affects 20-54 % of diabetes, leading to ocular irritation and blurry vision. Decreased conjunctival goblet cell mucus secretion is one of the major pathological processes of DMDES. This study aims to investigate the mechanism of mucus granule maturation and secretion disturbance in DMDES.

METHODS

Tear samples from diabetic patients with and without dry eye syndrome were analyzed by mass spectrometry to identify proteins associated with ocular mucous layer reduction. The N-terminal domain fragment of Mucin1 (MUC1-ND) was transfected into the mouse conjunctiva to investigate alterations in goblet cell mucus secretion. Protein localization and granule morphology were explored through transmission electron microscopy with colloidal gold labeling and immunohistochemistry. Immunofluorescence, co-immunoprecipitation, and integrative computational modeling of protein interactions were employed to explore protein-protein interactions.

RESULTS

Tear proteomic analysis revealed significantly elevated MUC1-ND levels in tears from DMDES patients, which correlated with reduced goblet cell mucus secretion and tear film instability. Upregulation of MUC1-ND in mice conjunctiva inhibited the maturation of secretory mucus granules, contributing to tear mucous layer reduction. Protein docking and co-immunoprecipitation analysis demonstrated that the binding of MUC1-ND and Syntaxin6 prevents granule fusion and maintains the immature state of secretory granules, which leads to reduced mucus secretion.

CONCLUSION

In DMDES, MUC1-ND binds with Syntaxin6 to disrupt the fusion and maturation of secretory mucus granules in conjunctival goblet cells, which provides a new insight into DMDES pathophysiology.